1. Field of the Invention
The present invention relates to a feed additive composition for ruminants. More precisely, it relates to a feed additive composition for ruminants, where a biologically active substance is coated with a coating composition which is stable in the rumen of ruminants and which releases the biologically active substance in the abomasum and the subsequent digestive tract of ruminants.
2. Description of the Background
When biologically active substances such as amino acids or vitamins are directly administered perorally to ruminants such as cattle or sheep, almost all of the substances are decomposed by microorganisms in the rumen of the ruminants which prevents effective absorption of the biologically active substance.
Therefore, rumen by-pass preparations, which protect such biologically active substances in the rumen of ruminants from decomposition by microorganisms so that the substances may be digested in and absorbed in the abomasum and the subsequent digestive tract, are important in the field of feeds, nutrients and animal drugs.
In preparing feed additives for ruminants which contain a biologically active substance, coating of the active substance with a protective substance such as fatty acids and hardened animal and vegetable oils has heretofore been proposed. However, if, a biologically active substance is coated with a sufficient amount of a protective substance so as to protect the active substance in the rumen of ruminants, it is difficult to achieve release of the active substance from the protective substance in the abomasum and the subsequent digestive tract.
In order to overcome the problem, a method has been proposed in which substances other than oils and fats, are added, which may enhance release of the biologically active substance from a protective coating substance. The method involves the dispersal and granulation of the active substance, and to the coating of the biologically active substance with the protective substance containing the additional substances.
For instance, U.S. Pat. No. 4,533,557 describes a method of dispersing a biologically active substance in a mixture comprising at least one member selected from hardened animal oils and fats, hardened vegetable oils and fats and saturated or unsaturated monocarboxylic acids, and chitosan, followed by granulating the dispersion. In the method, chitosan, which may dissolve or swell under acidic conditions, is utilized. However, since the dispersed biologically active substance exists also on the surface of the grains or near the surface thereof, the thickness of the coated layer is not even and some areas of the coated layer are very thin. In general, therefore, the stability of the biologically active substance in the rumen is low. In order to increase stability, the active substance must be coated with a fairly large amount of the protective agent, which, however, adversely diminishes the rate of release of the active substance. In the examples shown in the U.S. patent, the granules which are well protected with a coating, exhibit a poor rate of release of the active substance therefrom, while those which have a high release capacity have a low protecting capability. Anyway, the known granules do not exhibit a satisfactory combination of protection and release characteristics.
Japanese Patent Application Laid-Open No. 60-168351 proposes a method of granulating a biologically active substance along with calcium carbonate in an amount of 20% by weight or more and aliphatic monocarboxylic acids and hardened oils and fats in an amount of 10% by weight or more. In view of the time in which it takes granules to pass through the abomasum of ruminants and in view of the rate of dissolution of calcium carbonate, the release of the active substance still involves some problems.
Japanese Patent Application Laid-Open No. 63-317053 proposes a method of coating a biologically active substance with a coating agent comprising aliphatic monocarboxylic acids, hardened oils and fats, lecithin and glycerin fatty acid esters. However the time in which it takes the coated substance to pass through the small intestines is short and the release of the active substance is not sufficient in view the emulsifying action of lecithin and glycerin fatty acid esters.
In addition, a method of coating a biologically active substance with a pH-responsive synthetic polymer has also been proposed which is based on the difference in the pH value between the rumen and the abomasum. However, in view of the use of an organic solvent for the coating and of the high price of the coating agent, the method cannot be said to be sufficiently satisfactory from the point of view of safety and economics.